The goal of this project is to develop at least two strains of miniature swine, each homozygous for a different set of histocompatibility antigens at the major histocompatibility locus (SL-A). The animals will subsequently be used for in vivo experiments in organ and tissue transplantation and as a source of large numbers of cells from which cell surface antigens can be isolated, purified, and characterized chemically. The breeding plan and typing will be continued. Lines will be established and separated, so that herds of any required size in each line can be produced. Experiments in collaboration with the Surgery Branch will be carried out in order to: 1) characterize the immune response to transplantation of skin, kidney and liver in pigs across defined histocompatibility differences, and 2) to determine the basis of liver allograft tolerance which has previously been reported in pigs. Studies of the SL-A antigens will be initiated at the biochemical level. These will center first on isolation and purification, and them on chemical and immunologic characterization.